1. Field of the Invention
The invention relates to a method of operating a refuse incineration plant having a combustion chamber containing a grate for receiving refuse and a boiler receiving hot flue gases for the combustion chamber.
2. Discussion of the Background
The operation and, in particular, the uniform generation of heat in oil-fired or coal-fired power stations does not present problems. It is achieved by means of uniformly introducing a quantity of fuel, whose quality is constant and known. In the case of refuse incineration plants, too, the main objective, apart from constant flue gas quality and quantity, is to keep the heat output constant. In the case of refuse or waste combustion plants, it is not possible to control the quantity of heat by means of the metered introduction alone since the composition and, consequently, the calorific value of the combustible material introduced varies considerably with time, from glass to paper to moist garden wastes. Accordingly, even the desire to keep the quantity of heat produced and, consequently, the steam constant presents problems. Even more problematic is the constant generation of heat while optimizing the other parameters, for example the flue gas quality.
According to a known method, an attempt is made to keep the generation of heat constant on the basis of measuring solely the quantity of steam. Such a procedure is unsatisfactory. In this method, value variations are obtained which have large amplitudes.
It is known that with a fairly large proportion of combustible material in refuse, more oxygen is required for the incineration in the combustion chamber. As a consequence, less oxygen is present in the flue gases. This fact has already been exploited by G. Schetter and E. Leitmeir. In VGB KRAFTWERKSTECHNIK 1987, page 132, 133, a firing control system is described in which the influencing variable refuse composition is reduced to such an extent that a comparatively uniform incineration process is guaranteed. For this purpose, the use of three mutually independent control circuits is proposed, the first two of which the authors have already tested and the third only existed as a work project. In control circuit 1, the refuse throughput was controlled on the basis of the oxygen content of the flue gas as a controlled variable. Control circuit 2 used the quantity of steam as controlled variable and acted on the primary air supply. The purpose of control circuit 3, which was in the development stage, would have been to incorporate the control of the secondary air into the system.
This known type of control is expensive and is not capable of guaranteeing the uniformity of the liberation of heat and, consequently, the quantity of steam to the extent desired in practice. Optimization of further parameters is not even considered.